Many studies of ectomycorrhizal fungal (EMF) communities have documented compositional shifts resulting from environmental perturbations such as nitrogen fertilization and atmospheric CO₂ enrichment. Given the highly diverse nature of EMF communities, to what degree do these changes in EMF communities have consequences for the movement of carbon and nutrients between plants, fungi, soil and the atmosphere? In this talk I will highlight a number of methodological approaches to tackling this question, and the emerging picture of morphological and functional diversity in ectomycorrhizal fungi. Field sampling strategies designed to examine EMF hyphae coupled with biochemical and molecular methods are providing insight into biomass, cellular structure and exploration strategies of EMF hyphae in forest soils. Renewed efforts to isolate a diverse suite of EMF taxa provide greater resources for investigating the diversity of EMF substrate utilization. Recent advances in the molecular physiology of symbiotic nutrient transfer also allow both field and lab - based inquiry into the allocation of carbn and nutrients between plants and EMF at the symbiotic interface. By combining data from these methods it becomes possible to begin linking EMF species to their physiological importance and symbiotic potential. Ultimately, this yields predictive power regarding the consequences of changing EMF abundances on the flow of carbon and nutrients between aboveground and belowground forest ecosystem compartments.